1. Attempted robbery
2. Seems to coherently remember the events, hence 15.
3. If he's alert, orientated to person/place/purpose/time, can understand the risks of refusing treatment and is competent (e.g. not under the influence, however 1 beer is not "under the influence," but competent can include other issues besides substance abuse), then yes. If he's not, then no. The problem I see is his language. Is this his normal word choice and verbal style or is it significantly influenced by substance use? Just because someone talks strangely doesn't mean he is or isn't competent. Location, socioeconomic class, education, and plenty of other intangibles will affect these. Heck, if we want to go by word choice, I'd argue that most people who post on EMS forums are not competent to refuse care, little less render it.
4. Could this be his normal mentation? Yes. Could this be abnormal? Yes.
5.Alcohol, THC, glue.